A pressure-sensitive recording material utilizing a color reaction of microcapsules is known. It is also known to further incorporate a photopolymerization composition in said microcapsules thereby to terminate the color reaction of the recording material. For example, Japanese patent application (OPI) No. 89915/77 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") discloses a light-sensitive and heat-sensitive recording material which is to be heated after exposure; and Japanese patent application (OPI) Nos. B 124343/82, 179836/82 and 197538/82 disclose a light-sensitive and pressure-sensitive recording material which is to be recorded by means of a combination of an exposure step and a pressure step. In these techniques, microcapsules containing a photopolymerization composition are entirely hardened due to exposure, which results in the occurrence of a difference in hardness between the thus hardened microcapsules and the other non-hardened microcapsules in the non-exposed part, which phenomenon is utilized as the recording element. More precisely, these techniques utilize such a phenomenon that the microcapsules are hardened and the color forming component does not move (diffuse) even under heat, or otherwise, the microcapsules are hardened and cannot be crushed under normal pressure. The photopolymerization composition to be contained in the microcapsules comprises a photopolymerizable compound and a photopolymerization initiator, and aromatic ketones and quinone compounds are used as the photopolymerization initiator. In particular, benzoin-alkylethers are exemplified.
Various kinds of photopolymerization compositions have heretofore been developed for various purposes and uses including printing inks, plates to be printed, resists for base plates to be printed, etc., and these conventional compositions may be utilized in a photographic material for a recording material. For example, Japanese patent publication No. 37377/70 (corresponding to U.S. Pat. No. 3,418,118) discloses the use of photopolymerization initiator composition comprising 2,4,5-triphenyl-imidazolyl dimer and a free radical former; and Japanese patent publication No. 38403/73 (corresponding to U.S. Pat. No. 3,549,367) discloses the use of a photopolymerization initiator composition comprising 2,4,5-triphenyl-imidazolyl dimer and p-aminophenylketone. These publications mention that the photopolymerization compositions containing said photopolymerization initiator system are highly sensitive.
Conventional photopolymerization compositions which have heretofore been developed contain, in general, a binder, and most of said compositions may form a relief image by development. However, in the case that the composition containing no binder is kept liquid until hardened but does not form any relief image after being hardened, as the recording material of the present invention, it has been noticed that those compositions which have heretofore been known to be highly sensitive are not always highly sensitive.
Accordingly, conventional recording materials which have heretofore been used have a light-sensitizing speed of some degree and are effective only in limited uses. Thus, it has been required to obtain some other recording materials having a higher sensitivity, which may be applied to broader uses and may be used in a more compact and small sized exposure apparatus.